Storage tanks are widely used for storing a variety of liquids. Some of these liquids are hazardous and can be corrosive and/or flammable. In particular, underground storage tanks are used extensively for the storage of liquid gasoline at retail gasoline stations. Typical underground storage tanks are constructed with structural accessories such as an entry way and access lines for filling, dispensing, and venting.
The entry way found on many underground storage tanks is either a cover bolted directly to the storage tank or is a manway built onto the storage tank with a cover on the manway. Either type of entry way is intended to permit ready access to the interior of the tank for inspection and repair purposes. With recent regulations requiring more frequent testing and inspection, it has become even more desirable to access the interior of the storage tank without having to excavate to the tank and dismantle all the access lines, pumps, etc. Manholes have been used to provide a direct route to a buried storage tank. However, access lines also need to be inspected and guarded against from leakage. All the access lines cannot fit within the manhole without creating a safety hazard and also creating a dismantling problem to access the entry way to the storage tank's interior. Moreover, the access lines require special containment and protection features mandated by law. The access lines described above are examples of structures through which liquids and vapors flow and all of which are normally located at the top of the tank.
The access line which has proved most troublesome to adequately ensure against spillage and leakage has been the line for periodically filling the storage tank. This line extends from ground surface to the underground storage tank. Spillage at ground surface level can occur when the line is accessed by a transport tank truck operator for filling of the storage tank. Extreme care must be taken so that minor drippings do not occur since even minor drippings from repeated fillings over a course of years can ultimately become excessive. Drip sumps around the ground surface level of the fill line have helped, but are not fully adequate.
Another problem experienced by the fill lines is that if made of steel, as is conventional, they tend to corrode from contact with surrounding soil. A drip sump which extended from ground surface to the storage tank would appear to solve the problems in that it would catch accidental drippings from the filling operation as well as protect the fill line from contact with the soil. However, a deep drip sump itself creates a problem in that debris which enters is difficult to remove because of the depth.
A large secondary containment area to encompasses all the access lines has been suggested. This would allow for better ingress to the area to reach the various fittings, remove debris, etc. However, any drippings such as from a filling operation which reach any such relatively large containment area, whether directly or indirectly, create a potentially dangerous situation. The drippings can vaporize and with the right vapor-oxygen ratio can explode if a spark or other ignition source is present such as from electrical equipment often contained at or near the storage tank's access lines. As can be appreciated, there are several requirements that must be considered in the designing of a containment system for access lines to an underground tank.
The service life of a storage tank system will vary, but eventually the tank and its access lines will leak. Leaks from the tank system often happen within a few years after the new tank and lines are installed, due to improper installation or flaws in the manufacturing of the tanks and lines. Leakage problems are particulary troublesome in that gasoline storage tanks are usually buried underground. Any leaks which develop are normally very slow initially and are very difficult to detect. Leaks from subterranean tanks or their accessories can result in a significant danger to the environment and health of nearby residents. Federal as well as local regulations govern the design and maintenance of such storage tanks.
There now has been discovered an assembly for enclosing a storage tank's entry way and other structural accessories which solves problems associated with many known manhole and containment systems. The present invention solves the problems inherent with existing tank systems. It is useful with new tank systems and as well as a retrofit to buried tank systems.